1. Field of the Invention
The invention relates to a curable adhesive based on a reactive acrylate and/or methacrylate copolymer.
2. Description of the Prior Art
German Pat. No. 2,524,197 discloses the use as an adhesive of a terpolymer, consisting of
20 to 45 weight percent of acrylonitrile and/or methacrylonitrile, PA0 45 to 70 weight percent of an acrylate with 1 to 12 carbon atoms in the alkyl radical, and PA0 1 to 10 weight percent of acrylic, methacrylic or itaconic acid, PA0 (a) 20 to 80 weight percent of a copolymer which is obtained by the polymerization of PA0 (b) 10 to 70 weight percent of epoxide resin and/or glycidyl group-containing phenol-formaldehyde resin, PA0 (c) 0.2 to 15 weight percent of a harder for component (b), which is effective when heated, and PA0 (d) 0 to 5 weight percent of an accelerator for the reaction of component (b) with components (a) and (c), PA0 (a) a copolymer, which is obtained by the polymerization of PA0 (b) one or more polyisocyanates and/or their partial conversion products with polyols, the molecule having to have at least 2 isocyanate groups on the average, PA0 (a) a copolymer, obtained by the polymerization of PA0 (b) one or more polyisocyanates and/or their partial reaction products with polyols, in which the molecule has, on the average, at least 2 isocyanate groups,
in which the sum of the monomers must amount to 100 weight percent and the copolymer obtained has a limiting viscosity of 0.1 to 0.8 (100 mL.times.g.sup.-1) at 20.degree. C. in chloroform. Optionally, the terpolymer may be in admixture with up to 35 weight percent of an epoxide resin or a glycidyl group-containing phenol-formaldehyde resin. This adhesive makes gluings of high shear strength and good peel strength possible. The adhesive may be used as a film for gluing metal surfaces together as well as for gluing plastic films to metal surfaces. The adhesives remain thermoplastic if they are free of epoxide resins or of glycidyl group-containing phenol-formaldehyde resins. In the presence of epoxide resins or of glycidyl group-containing phenol-formaldehyde resins in the adhesive, the adhesives are heat-curable at temperatures of about 130.degree. C. Patent application (P No. 29 26 284.8-43) not yet published discloses a heat-curable adhesive containing:
(a.sub.1) 20 to 45 weight percent of acrylonitrile and/or methacrylonitrile,
(a.sub.2) 35 to 65 weight percent of one or more alkyl esters of acrylic and/or methacrylic acid with 1 to 12 carbon atoms in the alkyl radical,
(a.sub.3) 10 to 20 weight percent of acrylic, methacrylic and/or itaconic acid,
(a.sub.4) 0 to 15 weight percent of acrylamide and/or methacrylamide,
in which the sum of the monomers must amount to 100 weight percent and in which the copolymer has a limiting viscosity of 0.1 to 0.8 (100 mL.times.g.sup.-1) at 20.degree. C. in methyl acetate,
in which the sum of (a) to (d) must amount to 100 weight percent, with the optional addition of the usual additives, such as, gluing auxiliaries, adhesion promoters, pigments and fillers.
Compared to the adhesives of German Pat. No. 2,524,197, these adhesives cure at temperatures of 100.degree. to 130.degree. C. By curing at such low temperatures, it is possible to keep the thermal stress on the plastics to be glued at a low level and to maintain the surface quality and gloss of the plastic. The composite materials of plastic and metal, obtained by the gluing, can be shaped in the usual manner without adversely affecting the adhesion.
Patent application No. P 30 24 869.2 discloses a heat-curable adhesive containing
(a.sub.1) 35 to 70 weight percent of one or more alkyl esters of acrylic and/or methacrylic acid with 1 to 8 carbon atoms in the alkyl radical,
(a.sub.2) 20 to 45 weight percent of acrylonitrile and/or methacrylonitrile,
(a.sub.3) 10 to 20 weight percent of one or more .omega.-hydroxyalkyl esters of acrylic and/or methacrylic acid with 1 to 5 carbon atoms in the alkyl radical, and
(a.sub.4) 0 to 15 weight percent of acrylamide and/or methacrylamide,
in which the sum of the monomers (a.sub.1) to (a.sub.4) must add up to 100 weight percent and the copolymer has a limiting viscosity of 0.5 to 0.6 (100 mL.times.g.sup.-1) at 25.degree. C. in methyl acetate, and
the components (a) and (b) being present in such a ratio that 1 to 1.5 isocyanate groups of component (b) correspond to 1 hydroxyl group of component (a). Optional conventional additives, such as, accelerators, gluing auxiliaries, pigments and fillers may also be present.
Such an adhesive is advantageous since it can be cured reactively at low temperatures, for example, at 80.degree. C. and lower, without disadvantageously affecting the adhesive properties of the cured adhesives, the resistance of the cured adhesives towards moisture and other weather resistant properties.